Persistence of space radiation induced cytogenetic damage in the blood lymphocytes of astronauts

Abstract

Cytogenetic damage was assessed in blood lymphocytes from 16 astronauts before and after they participated in long-duration space missions of 3 months or more. The frequency of chromosome damage was measured by fluorescence in situ hybridization (FISH) chromosome painting before flight and at various intervals from a few days to many months after return from the mission. For all individuals, the frequency of chromosome exchanges measured within a month of return from space was higher than their preflight yield. However, some individuals showed a temporal decline in chromosome damage with time after flight. Statistical analysis using combined data for all astronauts indicated a significant overall decreasing trend in total chromosome exchanges with time after flight, although this trend was not seen for all astronauts and the yield of chromosome damage in some individuals actually increased with time after flight. The decreasing trend in total exchanges was slightly more significant when statistical analysis was restricted to data collected more than 220 days after return from flight. When analysis was restricted to data collected within 220 days of return from the mission there was no relationship between total exchanges and time. Translocation yields varied more between astronauts and there was only a slight non-significant decrease with time after flight that was similar for both later and earlier sampling times.

Introduction

During spaceflight, astronauts are exposed to very penetrating radiation consisting primarily of high-energy protons and heavy nuclei, and secondary radiation created by interaction of nuclei with shielding material [1]. Yields of chromosome damage in astronaut's peripheral blood lymphocytes have been shown to increase after long-duration space missions of a few months or more, providing a useful in vivo marker of space radiation induced biological damage [2], [3], [4]. Biological dose estimates derived from frequencies of chromosome exchanges using preflight in vitro calibration curves and estimates derived from samples collected a few days after return to earth lie within the range expected from physical dosimetry and International Commission on Radiation Protection (ICRP) models [5]. Moreover, if radiation induced chromosome translocations persist in peripheral blood lymphocytes for many years, as has been commonly believed, they could potentially be used to measure retrospective doses or prolonged low dose rate exposures. However, recent evidence suggests that the yield of translocations may decline with time after irradiation, at least for space radiation exposures [6], [7]. Durante et al. [7] analyzed chromosome damage in Russian cosmonauts and reported a lack of correlation between time in space or absorbed dose and translocation yields, although no individual time dependence of translocations was presented in this study. In our previous study of six astronauts [6], blood lymphocytes were collected at various times after return from long-duration missions onboard the International Space Station (ISS) and five astronauts showed temporal declines in yields of chromosome damage with individual half-lives ranging from 10 to 58 months. In the present paper we describe more extensive follow-up measurements of chromosome aberrations in the blood lymphocytes of 16 astronauts assessed by FISH painting and collected at various times beginning directly after flight. The increased sample population gives more comparative information on individual temporal responses and allows us to perform more robust statistical analysis. The yields of total exchanges were compared with yields of mono-centric or so called “stable” aberrations. Since stable chromosome exchanges do not impose mechanistic interference to cell division, lymphatic stem cells should be able to produce new lymphocytes containing stable aberrations, and yields of this type of exchange are, therefore, considered to be stable with time. Data from two time internals after flight were considered separately to determine if results from early time points were consistent with results from later collection times.